Prior Art
The present invention relates to a process and apparatus for making fine-scale patterns on resist films or the like on substrates such as semiconductive wafers.
In general, the photolithographic techniques have been used in order to make fine-scale patterns in the production of semiconductive devices by imaging a mask pattern of ultraviolet light onto a resist film or the like on a wafer. However when the width of a line becomes less than two microns, sharp definition cannot be obtained because of the diffraction of ultraviolet light. In order to overcome this drawback, deep ultraviolet rays, X-rays or an electron beam is used to make patterns consisting of lines with a width less than two microns. The materials which are sensitive to such rays are called photo resists, X-ray resists and electron beam resists, respectively.
The most important characteristics which determine the quality of resists are resolution or resolving power and sensitivity. The term "sensitivity" refers in this specification to "the level of exposure received by a resist whereby in the case of the positive type the resist at the exposed area is completely dissolved away or in the case of the negative type the resist in the exposed area remains undissolved". The term "resolving power" refers in this specification to "the minimum width of a line drawn". In general, the resists having a high resolving power have a poor or low sensitivity, and vice versa. A resist with a low sensitivity needs a high-intensity exposure in terms of the radiation energy per unit area. However, in practice, the resists must have both a high resolving power and a high sensitivity especially when lines with a width less than one micron are drawn. Especially the electron beam and X-ray resists must have such characteristics.
As compared with photolithography, the electron beam or the X-ray beam used in drawing fine-scale patterns on the resist films or the like has a small current density or a small dose so that a long exposure time is required, which is one of the most adverse factors influencing the mass production of semiconductor devices. Therefore, in the technology for drawing fine-scale patterns by electron beam, increasing the pattern drawing speed is the most pressing problem. Another problem is the elimination of the proximity effects due to "the action through medium" (which is very similar or very closely analogous to the intermittency effect in some sense) to be described in detail below.
In view of the above, one of the objects of the present invention is to provide a process for making fine-scale patterns on a resist film or the like which may drastically improve the apparent sensitivity of the resist film or the like used, whereby the desired effects may be attained which otherwise could never be attained without the use of an ideal resist material having both a high sensitivity and a high resolving power.
Briefly stated, the fine-scale pattern making process in accordance with the present invention comprises the steps of subjecting a resist film or the like to an exposure of an intensity less than the sensitivity of the resist film or the like and making desired fine-scale patterns (the step referred to as "the pattern making exposure" in this specification), whereby the pattern drawing speed may be considerably increased and the proximity effects due to the "action through medium" may be substantially eliminated.